First generation analog-based mobile tele-communication systems generally use a pair of dedicated radio channels with typically 30 kilo-Hertz (kHz) bandwidth to establish connection between the base station (BS) and mobile station (MS). Second generation, digital wireless telecommunication systems such as those conforming to the Global System for Mobile Communication (GSM) or Interim Standard 136 (IS-136), employ a time division multiple access (TDMA) approach in which each pair of dedicated radio channels convey a number of connections between the mobile station(s) and the base station, with each mobile station being allocated a timeslot on the channel. In those systems, the radio channel bandwidth is larger—for example, 200 kHz for GSM systems.
Code division multiple access (CDMA), used in Interim Standard 95 (IS-95) or Universal Mobile Tele-communication System (UMTS) Terrestrial Radio Access Frequency Division Duplex (UTRA FDD) mobile tele-communication systems, are spread spectrum systems employing a pair of radio channels with much larger bandwidth than either first or second generation systems—that is, 1.5 mega-Hertz (MHz) for IS-95 and 5.0 MHz for UTRA FDD. Each band conveys communications for multiple users, with each user assigned a pseudo-noise (PN) random sequence constructed from channelization and scrambling codes by which information is modulated as “symbols” onto the channel. A receiver having knowledge of the PN code for a particular user is able to distinguish that user from the others.
A typical wireless system includes a transmitter where information bits are encoded by a channel encoder and modulated by a modulator for transmission through a wireless communication channel having fading and additive white Gaussian noise (AWGN). A typical wireless receiver operating on wireless signals received from the channel includes an inner modem, such as a rake receiver in a UMTS Frequency Division Duplex (FDD) system, and a channel decoder to correct errors introduced by the channel. The receiver performance depends, to a large extent, on the performance of the channel decoder. A channel decoder working with a soft decision has approximately 3 decibels (dB) gain over a channel decoder working over hard decision input. However, that 3 dB gain can be lost without proper input of the received wireless signal to the channel decoder.
There is, therefore, a need in the art for a method of ensuring receiver performance in a wireless communication system.